A comprehensive morphological investigation of selected species of organisms in the order Mycoplasmatales is proposed. The organisms will be studied in terms of three dimensional morphology, ultrastructure, and replication. Organism/cell interactions will be investigated by use of tissue culture cell lines and alveolar macrophage systems in vitro. The relationships between cell and organism will be assessed by light microscopy, electron microscopy and scanning electron microscopy. Mycoplasma/virus systems will be studied during development on solid media and in fluid media. Methods for the quantitation of these interactions will be used where applicable.